Systems and methods for the schedule alignment of a packet flow

ABSTRACT

A classification mechanism automatically aligns time-sensitive data streams to sequences (schedules), according to information in the packets or other information and classification criteria specified by a human network administrator, a sequence agent, an application program or otherwise. When a packet arrives at a first sequence-aware switch along a path, the packet is aligned to a new or existing sequence. When a new sequence is established, appointments are reserved at sequence-aware switches along the path. The packet is placed in a queue, based on its classification. When the packet reaches the head of the queue, at that queue&#39;s appointment time, the switch forwards the packet along the path. If possible, appointments have been reserved at subsequent switches along the packet&#39;s path, so the packet can be forwarded through the subsequent switches without delay. Packets that do not match any classification criteria are handled on a best-effort basis.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/501,391, entitled “Systems and Methods for the Schedule Alignment ofa Packet Flow,” filed Sep. 9, 2003.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

(Not applicable)

BACKGROUND OF THE INVENTION

The present invention relates to transmission and switching of datapackets through computer networks, such as scheduled packet switchingsystems, and more particularly to automatic scheduling of data flows.

So-called “converged” computer networks carry a mixture of traffictypes, such as data, telephone (voice) and video. Some of this trafficis time-sensitive, and other of the traffic is not time-sensitive. Forexample, a converged local area network (LAN) can include a variety ofhosts, such as workstations, IP telephones, storage servers, printservers, web servers, telephony servers (PBXs) and other endpoints. TheLAN typically includes switches, routers, etc. (collectively“switches”), links between the switches and other network elements thatinterconnect the workstations, IP telephones, servers, etc. Timelydelivery of packets that carry voice information between IP telephonesand telephony servers is important to providing high-quality voicesignals. Similarly, video and other time-sensitive packets must bedelivered without delay. On the other hand, delays are tolerable in thedelivery of normal computer data.

Some networks are operated as “real-time network scheduled packetrouting systems” (or simply “scheduled networks”), so time-sensitivepackets can be delivered without delay or jitter. One such system,described in U.S. Pat. No. 6,556,564, essentially reserves recurringtime slots (“appointments”) at “schedule-aware” switches for eachtime-sensitive stream of packets (called a “scheduled data flow”)between a pair of endpoints. When an application program executing on ahost connected to the network wishes to establish a path to another hostfor delivering a time-sensitive stream of packets, the application sendsa request to a “scheduling agent” to establish a scheduled data flow.The path between the hosts (endpoints) includes one or more switches, arespective link between each pair of switches along the path and ingressand egress ports where the links terminate at the switches. The switchesforward packets received on the ingress ports to the egress ports. Anetwork can carry many crisscrossed scheduled data flow paths.

Each egress port has an associated schedule, in which individualrepeating appointments can be made to reserve the egress port on aperiodic basis for a particular scheduled data flow between a particularpair of endpoints. Reserving the egress port also reserves resources(within the switch) that are used to pass data received on an ingressport to the egress port. The scheduling agent makes the appointments(reserves the egress ports of the switches) along the path andcoordinates the times of the appointments, such that (to the extentpossible) when a packet is expected to be received on an ingress port ofa switch, the appropriate egress port on the switch is reserved for thescheduled data flow. Thus, the packet can be forwarded by the switchwithout queuing the packet within the switch. Non-scheduled traffic thatwould otherwise be sent out the egress port is held off (queued withinthe switch), so the non-scheduled traffic does not interfere with thescheduled data flow.

In an ideally scheduled path, all egress ports along the path from oneendpoint to the other endpoint are scheduled such that each egress portis reserved at a time that is equal to the reservation time of theimmediately preceding egress port along the path, plus propagation timeof a packet from the preceding egress port. Thus, a packet can traversethe path, from one endpoint to the other endpoint, without any queuingdelay within any switch along the path. Due to the sequential nature ofthe reservation times along the path, the term “sequence” is usedsynonymously with “schedule” elsewhere in this disclosure.

During appointment times that are not reserved for any scheduled dataflow, and during reserved appointments during which the switch does notreceive a packet of the scheduled data flow, the switch routesnon-scheduled traffic on a best-effort basis, as in more traditionalswitches. The switches can detect unused reserved appointments. Forexample, if the beginning of a packet does not arrive at a switch withina predetermined amount of time after the beginning of an appointment,the switch can conclude that no scheduled packet will be received duringthat appointment.

Scheduled networks ensure jitter-free delivery of time-sensitive packetswhile providing traditional best-effort delivery of non-time-sensitivepackets. However, only application programs that explicitly requestscheduled data flows receive this expedited service. These applicationprograms must, therefore, be written to make these requests.Furthermore, to make application programs potable (i.e. capable of beingused with scheduled networks and more traditional networks that do notinclude scheduling agents and schedule-aware switches), the applicationprograms must be written to ascertain the kind of networks they operatewith and make (or not make) requests for scheduled data handling, asappropriate. In addition, the performance of many existing (legacy)application programs would be improved by utilizing scheduled dataflows, but these programs lack logic to request such service.

In addition, scheduled networks, and traditional best-effort networks,cannot be heavily utilized for non-time-sensitive traffic, withoutqueuing packets within the switches. Heavy utilization is desirable, inthat it is a cost-effective use of network elements. However, theconsequential packet queuing consumes resources within many or all ofthe switches, and it causes delays in the delivery of the packets.

Some network owners would appreciate network elements that canautomatically provide scheduled data flows to time-sensitive datastreams, without explicit requests to do so from application programs.

BRIEF SUMMARY OF THE INVENTION

The present invention includes methods and apparatus that canautomatically align a time-sensitive data stream to a sequence(schedule), without an explicit request to do so from an applicationprogram. These methods and apparatus are applicable in networks thatcarry only non-time-sensitive traffic, only time-sensitive traffic ormixtures of both types of traffic.

In accordance with the present disclosure, a classification mechanismautomatically identifies individual packets or data flows of packets(collectively “data flows”) that should be sequenced and sequences thedata flows. The data flows can be classified according to information inthe packets or other information. Classification criteria can bespecified by a human network administrator, a sequence agent, anapplication program or otherwise. The criteria can be used to identifyone or more classes of data flows. A data flow that matches someclassification criteria can be aligned to an existing sequence, or a newsequence can be established for the data flow. When a new sequence isestablished, a sequence agent reserves appointments at sequence-awareswitches along the path. Because packets in sequenced data flows incurlittle or no queuing in switches along their respective paths betweenendpoints, the now-sequenced packets move through a network moreexpeditiously. Packets that do not match any classification criteria arehandled on a best-effort basis.

In one embodiment, the network includes sequence-aware switches and canoptionally include non-sequence-aware switches. Packets of a data floware carried from a source endpoint, over a path through the network, toa destination endpoint. When one of these packets arrives at the firstsequence-aware switch along the path (or a segment of the path, asdescribed below), the packet is classified for sequenced ornon-sequenced handling. Thus, the source endpoint and source applicationneed not request sequenced handling for this data flow. In fact, thesource endpoint and source application need not even be aware thatsequenced handling is available. Consequently, legacy applications canautomatically benefit from this expedited handling, withoutmodifications to the applications.

If a packet is classified for sequenced handling, the switch places thepacket in an appropriate queue, based on the classification. When thepacket reaches the head of the queue, at that queue's appointment time,the switch forwards the packet along the path. If possible, appointmentshave been reserved at subsequent switches along the packet's path, sothe packet can be forwarded through the subsequent switches withoutdelay.

If the packet subsequently reaches a non-sequenced segment of the path,i.e. a segment made up of non-sequence-aware switches, the packet isforwarded by these switches in a best-effort fashion. If the packetsubsequently reaches another sequenced segment, the packet isclassified, queued, etc. (as described above) again. The packet can beclassified (and thus handled) differently in the second sequencedsegment than in the first sequenced segment. In either case, legacynetwork elements, such as non-sequence-aware switches, can be combinedwith sequence-aware network elements in a composite network. Otherfeatures, functions and aspects of the invention will be evident fromthe Detailed Description of the Invention that follows.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

These and other features, advantages, aspects and embodiments of thepresent invention will become more apparent to those skilled in the artfrom the following detailed description of an embodiment of the presentinvention when taken with reference to the accompanying drawings, inwhich the first digit, or first two digits, of each reference numeralidentifies the figure in which the corresponding item is firstintroduced and in which:

FIG. 1 is a simplified block diagram of an exemplary communicationsnetwork in which an embodiment of the present invention can bepracticed;

FIG. 2 is a simplified block diagram of a sequenced switch of FIG. 1;and

FIG. 3 is a simplified flow diagram of a method of operating thesequenced switch of FIGS. 1 and 2.

DETAILED DESCRIPTION OF THE INVENTION

U.S. Provisional Application No. 60/501,391, filed Sep. 9, 2003,entitled “Systems and Methods for the Schedule Alignment of a PacketFlow,” is incorporated herein by reference.

U.S. patent application Ser. No. 09/746,744, filed Dec. 22, 2000,entitled “Network Switch With Packet Scheduling,” is incorporated hereinby reference.

U.S. Provisional Patent Application No. 60/349,115, filed Jan. 16, 2002,entitled “System And Methods For Achieving High Availability OfItineraries In A Real-Time Network Scheduled Packet Routing System,” isincorporated herein by reference.

U.S. patent application Ser. No. 10/162,454 filed Jun. 4, 2002 entitled“Real-Time Network Scheduled Packet Routing System,” is incorporatedherein by reference.

U.S. Pat. No. 6,556,564, issued Apr. 29, 2003, entitled “ScheduledInternet Protocol Telephone Instrument System,” is incorporated hereinby reference.

U.S. patent application Ser. No. 10/900,986, filed Jul. 28, 2004,entitled “Systems and Methods for the Synchronization of a Real-TimeScheduled Packet Network Using Relative Timing,” is incorporated hereinby reference.

The present application discloses methods and apparatus thatautomatically align a time-sensitive data flow to a sequence (schedule),without an explicit request to do so from an application program. In oneembodiment, the data flow is classified, based on an estimate of whetherthe data flow would benefit from sequenced routing through a series ofswitches along at least a portion of a path from a source endpoint to adestination endpoint. Classification criteria can be specified by ahuman network administrator, a sequence agent, an application program orotherwise. If the data flow meets some of the classification criteria,the data flow is aligned to an existing or new sequence along the path.The data flow can share a sequence with other data flows or the dataflow can be allocated its own sequence. In some embodiments, networkelements automatically classify data flows, as outlined above, as wellas accept explicit requests from application programs for sequencedhandling of their data flows, as discussed in the above-cited patentsand applications.

The classification can be based on information about the data flow, suchas information within packets of the data flow, information obtained bya network element about one or both endpoints or application programs atthe endpoints, historical network traffic statistics or any informationthat can indicate whether the data flow would benefit from sequencedhandling. For example, this classification can be based on: whether theprotocol used within the data flow is commonly used for real-timecommunication or for less time-sensitive communication; a hypothesisconcerning the type of application (for example, voice over IP (VoIP),video over IP, web browsing, etc.) generating the data flow; or measuredparameters, such as burstiness, of the data flow, optionally as comparedto quality of service (QoS) requirements (such as delay, jitter, packetloss, etc.) inferred by a network element or requested by theapplication.

FIG. 1 illustrates an exemplary communication network in which anembodiment of the present invention can be advantageously practiced. Thenetwork includes a number of endpoints 100, 102, 104, 106, 108 and 110.Some of the endpoints are sequenced endpoints, such as sequencedendpoints 102, 106 and 110. Other of the endpoints can be non-sequencedendpoints, such as non-sequenced endpoints 100, 104, and 108. Theendpoints 100-110 are interconnected by a combination of (non-sequenced)switches 112, 114 and 116 and sequenced switches 118, 120, 122, 124, 126and 128, as well as a number of links, such as links 130-158.

The sequenced switches 118-128 process packet flows based on scheduledarrival times, as discussed in the above-cited patents and applicationsand as summarized below. An endpoint, for example sequenced endpoint102, can initiate a data flow to one or more other sequenced endpoints,such as sequenced endpoint 106. The initiating sequenced endpoint 102sends a request to a sequencing agent 160 to establish a sequenced pathbetween the endpoints 102 and 106. The sequencing agent 160 selects acontiguous set of links, for example links 130, 132 and 134, for a pathbetween the endpoints 102 and 106. The sequencing agent 160 schedulesappointments at egress ports (not shown) on the sequenced switches 118and 122 that correspond to the links 132 and 134, respectively, of thepath. This processes is referred to as “sequencing.”

Each egress port on each sequenced switch 118-128 repeatedly executes a“schedule,” which represents a fixed amount of time or a fixed amount ofdata flow through the port. For example, a port can repeatedly cyclethrough a 20 mSec. schedule. Each schedule is partitioned into a set ofappointments. For example, a 20 mSec. schedule on a 100 Mb/Sec. port canbe partitioned into 1000 250-byte appointments. Appointments can,however, vary in size. Scheduling an appointment on a port reserves theport for a particular sequenced data flow at the appointment time duringeach subsequent 20 mSec. schedule, until the appointment is canceled.

Each appointment is a placeholder for one or more data packets.Sequenced switches 118-128 in the network are synchronized, such as to acommon clock, and all these switches and the links interconnecting themcycle through their appointment schedules. Clocks in the sequencedswitches 118-128 (and optionally the sequenced endpoints 102, 106 and110) can be synchronized by distributing “heart beat” synchronizationpackets, as described in U.S. patent application Ser. No. 10/900,986.For example, a “master” switch or other central time source can send theheart beat packets down a tree structure that includes the sequencedswitches 118-128 and the sequenced endpoints 102, 106 and 110. Thefrequency at which the heart beat packets arrive at the sequencedswitches 118-128 and the sequenced endpoints 102, 106 and 110 can beused to set local frequency references (clocks) in the switches andendpoints, such as through the use of digital phase-lock loops. As eachscheduled packet in a data flow arrives at a sequence-aware switch118-128, the switch transmits the packet on the appropriate outboundport at the designated appointment time, i.e. according to the port'sschedule.

The sequencing agent 160 makes the appointments (reserves the egressports of the sequenced switches 118-128) along the path and coordinatesthe times of the appointments, such that (to the extent possible) when apacket is expected to be received on an ingress port of a sequencedswitch 118-128, the appropriate egress port on the switch is reservedfor the sequenced data flow. Thus, the packet can be forwarded by thesequenced switch 118-128 without queuing the packet within the switch.When selecting the time for the egress port appointment, the sequencingagent 160 considers link transport delays, i.e. the delay between thetime the packet is sent out the egress port of the previous sequencedswitch 118-128 along the path and the time the packet arrives at thecurrent switch and is ready to be forwarded out the egress port of thecurrent switch. Thus, ideally, as soon as a packet begins accumulatingat the sequenced switch's 118-128 ingress port, the packet is cutthrough to its appointment on the egress port.

Non-sequenced traffic that would otherwise be sent out the egress portis held off (queued within the sequenced switch 118-128), so thistraffic does not interfere with the sequenced data flow. However, assoon as the scheduled packet transmission is complete, the egress portis made available for non-sequenced traffic. Thus, if the sequencedpacket transmission does not utilize the entire appointment, theremainder of the appointment is available for non-sequenced traffic.

Sometimes, an endpoint does not utilize every appointment, i.e. theremay be appointments during which the endpoint does not send any packets.The sequenced switch 118-128 detects this lack of packets. A portion ofthe beginning of each appointment is designated a “guard band.” If nopacket starts arriving during the guard band, the sequenced switchassumes no packet was sent during this appointment, and the switch usesthis appointment for non-sequenced traffic.

The sequencing agent 160 maintains a global database of appointments. Ifthe sequencing agent 160 cannot schedule the appropriate egress port forthe same time as the packet is expected to be received on the ingressport, the sequencing agent reserves the next available appointment onthe egress port's schedule. In this case, the sequenced switch 118-128queues the received packet between the time the packet is received onthe ingress port and the appointment time on the egress port. This delayis referred to as a “phase shift.”

Thus, each sequenced data flow has a reserved appointment (or pluralappointments, if the packet is too large for a single appointment or ifmultiple packets are sent together or in rapid succession during eachscheduled transmission time) at each egress port along all or part ofits path between the endpoints. The sequence of (appointment, egressport) pairs for a sequenced data flow is called its “itinerary.” Afteran itinerary is establish, as each packet in a sequenced data flowarrives at a sequenced switch 118-128, the switch transmits the packeton the appropriate egress port at the appointment time. Becausesequenced packets are rarely or never placed in stochastic queues (wherethey would contend for service with other packets), they do notexperience queuing delays, nor do they risk being dropped because aqueue is full.

As noted, a non-sequenced endpoint, such as endpoint 100, does notcontain logic to request the sequencing agent 160 to establish asequenced path. Such a non-sequenced endpoint simply initiatescommunication to another endpoint, such as non-sequenced endpoint 108.According to one aspect of the present disclosure, the sequencedswitches 118-128 are configured to classify data flows passing throughthe switches according to some criteria. The sequenced switches 118-128are also configured to use a data flow's classification to selectivelyalign the data flow with an existing or new sequence or to allow thedata flow to be handled on a best-effort basis.

The classification criteria can be provided to the sequenced switches118-128 by the sequencing agent 160. In one embodiment, the sequencingagent 160 includes a user interface 162, by which a networkadministrator can enter the classification criteria. In anotherembodiment, the sequencing agent 160 automatically determines theclassification criteria, such as by monitoring traffic patterns on thenetwork. Other embodiments can use other algorithms or heuristicsexecuted by the sequencing agent 160, an application program executed byone of the endpoints 100-110 or another element in the network (notshown) to determine the classification criteria. Examples ofclassification criteria are described in more detail below. When thesequencing agent 160 provides classification criteria to the sequencedswitches 118-128, the sequencing agent also establishes an itinerarythat corresponds to a data flow(s) matching the classification criteria.

When a packet arrives a sequenced switch 118-128, the switch classifiesthe packet and processes the packet accordingly. FIG. 2 is a simplifiedschematic block diagram of a sequenced switch 200, such as one of thesequenced switches 118-128 of FIG. 1. A packet classifier 202 classifiesincoming packets, as outlined above. This classification can involveexamining information within the packet for data that matches selectioncriteria or to form hypotheses regarding the data flow, of which thispacket is a part. This packet examination can involve any layer orlayers in the Open System Interconnection (OSI) protocol layer. Forexample, packet classification can involve examining Layer 2, such as todetermine the packet type, such as Ethernet, Point-to-Point Protocol(PPP), High-level Data Link Control (HDLC), Asynchronous Transfer Mode(ATM) or Frame Relay. Packet examination can also involve Layer 3, suchas to determine if the packet is (for example) an Internet Protocol (IP)or Internetwork Packet Exchange (IPX) packet. Packet examination canalso involve Layer 4, such as to determine if the packet is (forexample) a User Datagram Protocol (UDP) or a Transmission ControlProtocol (TCP) packet. Packet examination can also occur at higherlayers, e.g., OSI Layers 5, 6, and 7.

Examples of fields within the packet that can be examined include: Layer2 source address, Layer 2 destination address, Layer 2 priority, Layer 2virtual circuit/LAN/tunnel identifier(s), Layer 2 type field, Layer 3source address, Layer 3 destination address, Layer 3 priority, Layer 3virtual circuit/LAN/tunnel identifier(s), Layer 3 type field, Layer 4source port and Layer 4 destination port. Classifications can be basedon an exact match between one or more packet fields (or portionsthereof) and prescribed criteria. Classifications can also be based onone or more packet fields (or portions thereof) falling withinprescribed ranges of values. In addition, classifications can be basedon a combination of exact matching and range matching. Furthermore,classifications can be based on logical combinations (i.e. ANDs and ORs)of several criteria. A data packet falling within any type ofclassification criteria or logical combination of classificationcriteria is referred to herein as “matching” the criteria.

Packets can be categorized according to a source-destination pair,between which the packets are sent. For example, packets be categorizedaccording to source-destination pairs of endpoints (hosts), ports onthese endpoints or application programs being executed by the endpoints.For example, consider a data flow that contains Voice-over-IP (VoIP)bearer traffic sent by one IP softphone to another IP softphone. Packetsin this flow can be distinguished from packets in any other flow by thesource and destination IP addresses in the IP headers and by the sourceand destination UDP port numbers in the UDP headers. If the source anddestination IP addresses are, e.g., 135.35.31.155 and 135.35.47.189,respectively, and the source and destination UDP port numbers are 16384and 16388, respectively, then any packet containing these four values inits IP and UDP headers is classified as belonging to this data flow(“matching the criteria”).

Within data flows between pairs of endpoints, ports, etc., the dataflows can also be more finely categorized. For example, UDP traffic isgenerally more time-sensitive than TCP traffic, thus these two types ofdata flows can be categorized differently. As noted with respect to FIG.1, a network administrator can enter the classification criteria throughthe user interface 162, and the sequencing agent 160 can forward thisselection criteria to the sequenced switch 200 (FIG. 2). By thismechanism, the network administrator can establish sequenced pathsbetween pairs of endpoints, ports, applications, etc., by specifyingsource and destination addresses as the selection criteria.

Similarly, the network administrator can establish selection criteria,by which the sequenced switches 118-128 (or the sequencing agent 160 oranother network element (not shown)) can automatically detect data flowsthat would benefit from sequenced routing through a series of switchesalong a path. For example, the sequenced switches 118-128 might detecttime-sensitive data packets (as indicated by their protocol types orotherwise evidenced by information in the packets or elsewhere)traversing a path made up of links 132 and 142. Even if these datapackets are not all sent by the same endpoints, nor destined to the sameendpoints, the sequenced switches 118-128 and/or the sequencing agent160 can group all or some of these data flows together and align themwith one or more existing or new sequences.

Returning to FIG. 2, if the received packet is categorized astime-sensitive or potentially benefiting from sequenced handling, thepacket is added to a schedule alignment queue that corresponds to thepacket's category. Each output port has an associated schedule-awaretransmitter. For simplicity, the sequenced switch 200 is shown with onlytwo schedule-aware transmitters 204 and 206, although other embodimentscan include other numbers of output ports and schedule-awaretransmitters. Each schedule-aware transmitter 204 and 206 can have oneor more schedule alignment queues 208 and 210, respectively. Eachschedule alignment queue 208 and 210 represents a different sequence(schedule), and the schedule-aware transmitter 204 or 206 removespackets from the heads of the queues, according to the respectivequeues' schedules. Each schedule alignment queue 208 and 210 cancorrespond to a path between a pair of endpoints, ports, applications,etc. or a portion of such a path. Alternatively or in addition, eachschedule alignment queue 208 and 210 can represent a different selectioncriteria, although packets matching more than one selection criteria canbe mixed in a single queue.

The schedule alignment queues 208 and 210 are preferably sized such thatthey do not overflow and, thereby, cause packets to be dropped. Theschedule alignment queues 208 and 210 are sized based on the type andamount of traffic expected to match their respective selection criteria.For example, it is well known by those skilled in the art that if aqueue is twice the size of a maximum jitter (i.e., the maximum delayvariation between packets) of a data flow, then the queue will notoverflow. Typically, the maximum jitter that a flow experiences duringits lifetime is not known beforehand, but the maximum jitter can beestimated. For example, jitter can be estimated by using a priorianalysis or by using timestamp information contained in Real-TimeTransport Protocol (RTP) headers used by applications, such as VoIP orVideo-over-IP. For example, because VoIP packet flows are typicallyisochronous (i.e., have zero jitter) at their sources, the maximumjitter experienced by a VoIP flow is likely be less than the jitterexperienced by a data flow transported using the TCP protocol. Dataflows transported by the TCP protocol are typically bursty (i.e., highlyjittered) at their sources. Alternatively, if queue buffer memory spaceis large compared to the expected number of sequenced data flows, thenthe queue sizes can be set to values that exceed expected maximum jittervalues.

All the schedule alignment queues 208 and 210 can be of the same size,or characteristic or anticipated properties of the data flows can beused to determine appropriate queue sizes. For example, the propertiesof a data flow can include: source and/or destination applicationprogram type (e.g., VoIP, FTP, HTTP, Video over IP, etc.), transportprotocol type (e.g., UDP or TCP), real-time v. non-real-time, burstinessof packet rate and QoS attributes (e.g., delay, jitter, packet loss,etc.), as well as considerations described above respect to classifyingpackets.

As noted, it may also be useful to know or be able to infer the type ofapplication that generates or receive a data flow. Several methods canbe used to infer an application's type. For example, for applicationsthat use the Real-Time Transport Protocol (RTP), payload typeinformation in the RTP header of the flow's packets can be used todetermine the application's type. For example, if the payload type valueis 34 (indicating that the payload is encoded using the H.263 videostandard), then the source can be assumed to be a videoconferencingapplication.

Another method involves examining the TCP/UDP port numbers within thepacket. Some port number values are assigned by the Internet AssignedNumbers Authority (IANA) standards organization (www.iana.org) for useby specific applications. Port numbers that are not assigned by IANA maybe used by any application, but often applications limit the portnumbers they use to some small range of values. Therefore, knowledge ofan application's port number usage rules may also be applied toidentifying the application type that generates a data flow.

Packets that are not classified into a schedule-aligned queue 208 or 210are forwarded by the packet classifier 202 to a packet switching device212, such as a switch, router, hub or similar device. The packetswitching device 212 forwards these non-sequenced packets based on oneor more header addresses in the respective packets and, optionally,based on one or more other packet fields. One of ordinary skill in thisart will recognize this function as a conventional routing function. Thepacket switching device 212 places these packets in one or moreunscheduled queues 214 and 216 associated with the respectiveschedule-aware transmitters 204 and 206. The schedule-aware transmitters204 and 206 process packets on the unscheduled queues 214 and 216 on abest-efforts basis, such as during appointment times that are notreserved for any sequenced data flow and during unused reservedappointments.

As noted, the schedule-aware transmitters 204 and 206 transmit packetsof sequenced data flows at reserved schedule times. The schedule-awaretransmitters 204 and 206 also transmit non-scheduled packets duringperiods when there is no conflict with scheduled packet transmissions.The schedule-aware transmitter 204 or 206 should, therefore, finishtransmitting a non-scheduled packet before a reserved time for ascheduled packet, unless it is known that no scheduled packet is to besent at the reserved schedule time.

A path between endpoints can include sequence-aware segments (comprisingone or more adjacent sequenced switches) mixed with non-sequence-awaresegments (comprising one or more adjacent non-sequenced switches). Theclassification and alignment described above can be performedindependently for each sequence-aware segment. For example, returning toFIG. 1, assume non-sequenced endpoint 100 initiates a data flow tonon-sequenced endpoint 108 over a path made up of links 138, 140, 142,146, 148, 150, 152, 154 and 156. This path includes two sequence-awaresegments: a first segment made up of links 142 and 146 and a secondsegment made up of links 152 and 154. (Similarly, sequenced endpoint 102can initiate a data flow to another sequenced endpoint 110 over a pathmade up of links 130, 132, 146, 148, 150, 152, 154 and 158. Such a pathalso includes two sequence-aware segments separated by at least onenon-sequenced switch 114 and 116.) Each of these sequence-aware segmentscan be managed by a separate sequencing agent, or both segments can bemanaged by a common sequencing agent.

Because the two sequence-aware segments are separated by at least onenon-sequenced switch 114 and 116, packet traversal times through thesenon-sequenced switches cannot be predicted, and the schedules of the twosequence-aware segments cannot be coordinated with each another.

A method of operating an embodiment of the presently disclosed system isillustrated in a simplified flow chart shown in FIG. 3. At 300,classification criteria are received, such as from a networkadministrator or from the sequencing agent. It should be noted that manysets of classification criteria, each corresponding to a sequenced dataflow, can be received over time. Alternatively or in addition, theclassification criteria can be automatically generated. For example, thesequenced switches 118-122, the sequencing agent 160 or another networkelement can monitor packets flowing through the network to detectpackets that might benefit from sequenced routing. For example, packetsthat include Real-Time Transport Protocol (RTP) headers, UDP traffic orthat are generated by a time-sensitive applications are candidates forsequenced routing. If the network element detects one or more of thesepackets, such as within a predetermined amount of time, the networkelement can examine the packets for some common identifyingcharacteristic(s), such as one or more fields that have similar oridentical contents among the packets of the data flow. The element canthen generate classification criteria from some or all of theseidentifying characteristics.

If all schedule alignment queues are to be of the same size, controlpasses from decision point 302 to 306. However, if not all queues are tobe of the same size, control passes to 304, where a queue size isdetermined for the sequenced data flow associated with the receivedclassification criteria. If the sequenced data flow is to use anexisting schedule alignment queue, and that queue is already ofsufficient size, no further queue adjustments are necessary. On theother hand, if it is determined that the queue size should be increasedto accommodate the additional sequenced data flow, the queue size isadjusted at 304.

A packet is received at 306. At 308, if the packet matches someclassification criteria, control passes to 312, where the packet isplaced in a schedule-alignment queue that corresponds to the packet'sclassification. On the other hand, if the packet does not meet any ofthe classification criteria for sequenced handling, control passes to310, when the packet is placed in an unscheduled queue based on packetheader addresses and optionally other packet fields.

At 314, if a request is received to end schedule alignment for this dataflow, control passes to 316, where the classification criteria for thisdata flow is deleted. Alternatively, if no traffic of a particularclassification is detected for a predetermined period of time, schedulealignment for the corresponding data flow can be automatically ended Onthe other hand, if no request is received to end schedule alignment forthis data flow, and the schedule alignment is not automatically ended,control passes back to 306 to await receipt of another packet.

It will be appreciated by those of ordinary skill in the art thatmodifications to, and variations of, the above-described system andmethod for schedule aligning a data flow can be made without departingfrom the inventive concepts disclosed herein. For example, a sequencedswitch can be implemented in part or in whole using hardware components,such as host transmitters and receivers controlled by transmit andreceive control logic and connected to transmit and receive packetqueues, controlled by one or more microprocessors executing software orfirmware stored in a memory, and interconnected by a crosspoint matrix.The sequenced switches and the sequencing agent can also be implementedin software, firmware, hardware or any combination thereof. Thoseskilled in the art should readily appreciate that programs defining thefunctions of the present invention can be delivered to a computer inmany forms, including, but not limited to: information permanentlystored on non-writable storage media (such as read only memory deviceswithin a computer such as ROM or CD-ROM disks readable by a computer I/Oattachment); information alterably stored on writable storage media(such as floppy disks and hard drives); or information conveyed to acomputer through communication media, such as via baseband signaling orbroadband signaling techniques, including carrier wave signalingtechniques, such as over computer or telephone networks via a modem.Accordingly, the invention should not be viewed as limited except by thescope and spirit of the appended claims.

1. A method of automatically switching time-sensitive data packets,comprising: providing classification criteria; receiving a data packet;classifying the data packet according to the classification criteria;and if the received data packet is classified as being time-sensitive,aligning the received data packet to a sequenced data flow.
 2. Themethod of claim 1, wherein classifying the data packet further comprisescomparing at least some of the contents of the data packet to at leastsome of the classification criteria and wherein a match between the atleast some of the contents of the data packet and the at least some ofthe received classification criteria indicates the packet is classifiedas being time-sensitive.
 3. The method of claim 1, wherein classifyingthe data packet comprises examining at least some contents of the datapacket.
 4. The method of claim 3, wherein examining contents of the datapacket comprises examining at least one of a Layer 2 source address, aLayer 2 destination address, a Layer 2 priority, a Layer 2 virtualcircuit/LAN/tunnel identifier, a Layer 2 type field, a Layer 3 sourceaddress, a Layer 3 destination address, a Layer 3 priority, a Layer 3virtual circuit/LAN/tunnel identifier, a Layer 3 type field, a Layer 4source port and a Layer 4 destination port.
 5. The method of claim 1,wherein classifying the data packet further comprises comparing adestination identifier in the packet to at least some of theclassification criteria.
 6. The method of claim 1, wherein classifyingthe data packet further comprises comparing a source and a destinationidentifier in the packet to at least some of the classificationcriteria.
 7. The method of claim 1, wherein classifying the data packetcomprises determining a type of the packet.
 8. The method of claim 7,wherein determining the type of the packet comprises determining whetherthe packet is one of an Ethernet, a Point-to-Point Protocol, aHigh-level Data Link Control, an Asynchronous Transfer Mode and a FrameRelay packet type.
 9. The method of claim 7, wherein determining thetype of the packet comprises determining whether the packet is one of anInternet Protocol and a Internetwork Packet Exchange packet type. 10.The method of claim 7, wherein determining the type of the packetcomprises determining whether the packet is one of a User DatagramProtocol and a Transmission Control Protocol packet type.
 11. The methodof claim 1, wherein classifying the data packet comprises classifyingthe data packet as being time-sensitive if a voice over IP applicationgenerated the data packet.
 12. The method of claim 1, whereinclassifying the data packet comprises classifying the data packet asbeing time-sensitive if a video over IP application generated the datapacket.
 13. The method of claim 1, wherein classifying the data packetcomprises classifying the data packet as being time-sensitive if thedata packet is a Real-Time Transport Protocol (RTP) packet.
 14. Themethod of claim 1, wherein classifying the data packet comprisesinferring an application type of an application that sent the datapacket.
 15. The method of claim 14, wherein inferring the applicationtype comprises examining at least some contents of the data packet. 16.The method of claim 15, wherein examining at least some contents of thedata packet comprises examining payload type information in the datapacket.
 17. The method of claim 15, wherein examining at least somecontents of the data packet comprises examining a port number in thedata packet.
 18. The method of claim 1, wherein classifying the datapacket comprises obtaining information about a source of the datapacket.
 19. The method of claim 1, wherein classifying the data packetcomprises obtaining information about a destination of the data packet.20. The method of claim 1, wherein classifying the data packet comprisesusing network traffic statistics.
 21. The method of claim 20, whereinusing network traffic statistics comprises measuring at least oneparameter of a data flow.
 22. The method of claim 21, wherein measuringthe at least one parameter comprises measuring a parameter selected froma list comprising burstiness, delay, jitter and packet loss.
 23. Themethod of claim 1, wherein providing the classification criteriacomprises receiving the classification criteria via a user interface.24. The method of claim 1, wherein providing the classification criteriacomprises receiving the classification criteria from a sequencing agent25. The method of claim 1, wherein providing the classification criteriacomprises receiving the classification criteria from an applicationprogram.
 26. The method of claim 1, wherein providing the classificationcriteria comprises generating the classification criteria based onmeasurements of network traffic.
 27. The method of claim 1, whereinaligning the received data packet to a sequenced data flow comprisesscheduling at least one appointment at at least one switch forsubsequent data packets that are classified as the received data packetis classified.
 28. The method of claim 1, wherein aligning the receiveddata packet to a sequenced data flow comprises enqueuing the data packetto queue that corresponds to the classification of the data packet. 29.The method of claim 28, wherein aligning the received data packet to asequenced data flow further comprises determining a size of the queuebased on an amount of traffic expected to be classified as the receiveddata packet is classified.
 30. The method of claim 29, wherein aligningthe received data packet to a sequenced data flow further comprisesdetermining a size of the queue based on an amount of jitter in a dataflow.
 31. The method of claim 29, wherein aligning the received datapacket to a sequenced data flow further comprises determining a size ofthe queue based on an estimate of an amount of jitter in a data flow.32. Apparatus for automatically switching time-sensitive data packets,comprising: a packet switching device; at least one schedule alignmentqueue; and a data packet classifier configured to: classify receiveddata packets according to classification criteria; and if a receiveddata packets is not classified as being time-sensitive, forward the datapackets to the packet switching device; and if the received data packetis classified as being time-sensitive, forward the data packet to one ofthe at least one schedule alignment queue.
 33. The apparatus of claim32, further comprising at least one schedule-aware transmitterconfigured to dequeue data packets from at least one of the at least oneschedule alignment queue and transmit the dequeued data packetsaccording to a schedule.
 34. The apparatus of claim 33, furthercomprising a sequencing agent configured to establish the schedule. 35.The apparatus of claim 33, further comprising a sequencing agentconfigured to provide the classification criteria.
 36. The apparatus ofclaim 35, further comprising a user interface connected to thesequencing agent configured to receive the classification criteria.